Tandem power unit for applying hydraulic pressure



.My E5, E952 E. A. RocKwELl.

2,603,066 TANDEM POWER UNIT FOR APPLY'ING HYDRAULIC PRESSURE Filed Aug. z2, 1945 2 SPEETSFSHEET l E. A. ROCKWELL July 15, 1952 2,603,066

TANDEM POWER UNIT FOR APPLYING HYDRAULIC PRESSURE Y Filed Aug. 22, 1945 SHEETS-SHEET 2 7 .7 9 .0 4 2l auf NW 0| xpm ..7 4 K\ 4 a M @E 2f.

W W 4 mm A 6 3 5 3 W 2, 6 a m /M I 6 0 f KMA r/ ///////w/ Y /r by W 54 f a 0 Patented July l5, 1952 TANDEM POWVER UNIT FOR APPLYING HYDRAULIC PRESSURE Edwardv A. Rockwell, Shaker Heights, Ohio, as-

signor, by mesne assignments, to Borg-Warner Corporation, Chicago, Ill., a, corporation of Illinois Application August'ZZ, 1945, Serial No. 611,985

16 Claims.

My invention relates rparticularly to power units designed for applying power for the operation of any desired apparatus, but which, for example, is especially useful in the operation of accessories on automobiles or airplanes, etc.

The object of my invention is to provide a power unit which is simple and effective in construction, and which may be applied advantageously for the operation of any desired apparatus, as, for instance, any ofthe accessories to be controlled on automobiles or airplanes, etc. A further object is to provide a power unit of this character, in which the different parts are arranged coaxially, thus simplifying the construction while maintaining the eifective control and operation of the power unit. Another object is to provide a simplified valve mechanism for the power unit and which may, for instance, include grommet valves for controlling the application of a fluid pressure to a movable wall operated thereby for placing a hydraulic liquid under pressure to be conveyed therefrom for the operation of the accessory. Another object of my invention is to provide a hydraulic plunger which is operable manually to control the said valves, and which'is arranged coaxially with the movable Wall aswell as with a hydraulic power plunger connected with the movable wall. A further object is` to provide a valve-operating stem connecting the manual plunger with the valves, and which passes through the hydraulic power plunger. Still another object is to provide an enclosed bushing for supporting the hydraulic power plunger from the cylinder provided for the movable Wall. A further object is to provide a cylinder or casing for the mov-A able wall, and a closureffor the same which is U-shaped in cross-section, which is guided on the cylinder and hasV an effective fastening means. Further objects of my invention will appear from the detailed description of the same hereinafter.

While my invention is capable of embodiment in many different forms, for the purpose of illustration I have shown only one form thereof in the accompanying drawings, in which-- Fig. 1 is a vertical section of a power unit made in accordance with my invention;

Fig. 2 is van enlarged section of the. valve mechanism for said power unit; and

Fig. 3 is an Aend elevation of the power unit as viewed from the right4 in Fig. 1. n

In the drawings, I have shown a pedal I mountedronfa pedal lever 2 carried by a xedpivot 3 on the chassis of an automobile, the samebeing (Cl. Gli-54.5)

connected by a pivot 4 to a piston rod orlinkv 5 which is connected to a piston 6; ina master cylinder 1 which has a port 8 leading to amaster cylinder reservoir 9 in the usual way. Apipe ID leads from vthe master cylinder lto an inlet I ILin a screw plug I2, having a seal I3',`screwthreaded into a cylinder I4. The screwplug I2, further-:- more, has four semi-cylindrical holes I5 bored in the inner end of the same so as to leave a central portion I6 to'act as a valve stop. The Stop I6 cooperateswith a squared stemll having fon its inner end a tapered valve I3 having ascrewe driver slot I9. Said valve I8 is normallyipressed towards thel right inthe direction of its position against a valve seat member 2D, which member has a seal 2I `and is held inplace by a split ring 22, .byl meansof a helical spring 23 carried on a removable pin 2d :having a flange 25 whichseats in a recess 2S in the end of a manually operable plunger 2l, in which the valve seatmember 2l): and the split ring 22 are carried. Radial ports 28 are located in the manual plunger 2l to permitlthe passage of hydraulic liquid past the valve I8,.2D, and thence into an annular space 29 around the manual plunger 2l which communicates with van inclined'passageway' 3B leading to a longitudinal passageway 3l and thence to a delivery port ,32 in a power plunger cylinder or casing 33. An annu-:- lar seal 34 is located between the passagewaysv 30 and 3i, and the cylinder I4 is `securedto the casing 33 by means of screws` 35. The Vplunger .27, furthermore, passes through an annular :seal

36 and atlits left hand end is providedr witha screw-threaded annular bushing .3.1, in the in# terior of which there is a sleevev 38 having a ange 39 to 'provide a support for a helical .spring 40, the other end of which rests against .ai-,shoulder 4I vin a cylindrical chamber 42 linsidevthe manual plunger 2l. Furthermore. a` valve-operating rod 43 passes through the bushing 38 and thence through the chamber 4-2 and intoa cylindrical recess-4i so that the end ofthe rod 43 abuts against the end of the said recess 44. A plurality Oi airports 45 lead from theouter-air to an annu.- lar chamber 46, in the casing 33,*which isV formed -by the presence of a. piston 47 fastened one-a power plunger rod 48, said'piston having aninner seal 49 andan outer seal 58 the latterY being fin contactwith the face of a power cylinder 5t and the interior of the casing lurthermoraat the extreme rig-ht hand end of the power plunger 48 there isan apertured Washer 52 yhaving* la series of holes 53 to permit the entryI of the airffrofm theV annular chamber 46 to, ay longitudinal passageway 54 located in the power plungerii.

It will be noted that the cylinder 5 I has a passageway 55 leading therefrom to the longitudinal passageway 3| and thence by the delivery port 32 from which the liquid placed under pressure by the piston 41 will be delivered through a hydraulic pipe 56 having branch pipes 51 and 58 which lead, respectively, to front and rear wheel cylinders 59 and 60, carrying pistons in the usual way for the operation of the brake shoes in cooperation with the brake drums (not shown).

In the left hand end of the casing '33.there is a bushing 6I having an external seal 62 and an internal seal 63. The bushing 6I has a flange 64 through which a series of screws 65 pass to clamp between the flange 64 and the casing 33 and end plate 66, U-shaped in cross-section, which is provided with a screw plug v61 for a trailer connection, when desired, or for testing purposes or for introducing oil to the interior of a cylinder 68, which has an opening 69 for connection to any suitable source of vacuum, as by a check valved pipe 10 to a manifold 1| of an internal combustion engine of the automobile on which the power unit herein described is mounted, for driving the automobile. The cylinder 68 has an annular ange 12 which is located over a cylindrical flangek 13 on the periphery of the end plate 66, which has an outwardly directed flange 14 for clamping a cylindrical seal 15 against the flange 12 by means of a circular channel`member`16, which has two ends 11 and 18 carrying sleeves 19 and 80, respectively, that are forced together by a bolt 8| having on its end a nut 82. The cylinder 68, furthermore, has a circular recess 83 for supporting one end of a conically shaped spring 84, the smaller end of which is supported against a valve casing shell 85 located on a movable wall, in the form of a pistion head 86 which has at its periphery a leather gasket 81 tted against the inside of the cylinder 68. retained in place by a spring ring-88, L-shaped in cross-section, and which has longitudinal alternating cuts 89 and 90 therein extendlng from the opposing sides of said ring 88. The ring' 88 is held against the leather gasket 81 by means of a spring disc 9|. The movable wall 86 and the spring disc 9| are both supported within a recess 92 on a valve casing member 93 to which they are fastened by means of screws 94 which extend, also, through the valve casing shell 85 and are-screw-threaded into a valve casing 95, which has a seal 96, screw-threaded on the end of thefpower plunger 48, where it is held in place by a lock screw 91.

' The left hand end of the valve rod 43 is slidably supported within a small bushing 98 fastened in the end of the valve casing shell 85, which is in communication by means of a port 99 to the interior of the cylinder 68. The bushing 98, furthermore, supports one end of a helical spring |00, the other end of which rests against one side of anannular valve member IOI which is held in place on the valve rod 43 by means of split rings |02 and |03 and sealed on said rod by means of a seal |04. The valve member I0| is located -inl a i centrally arranged vchamber |05 in the valve casing member 93, said chamber |05 being conthe inner faces of which there are provided spring supporting rings III and II2 for supporting the ends of a helical spring II3, which normally presses the two flanges |09 and IIO away from each other and against the Valve casing shell and the valve casing member 93, respectively. A ring I|4 occupies a circularinner recess II5 in the rubber vacuum valve |08 to hold the same outwardly towards the periphery of the valve casing member 93.

On the other side of the valve element IOI there is, furthermore, provided an annular flange |I6 which cooperates with a grommet air valve I|1, made of rubber, that is constructed just the same as the grommet vacuum valve |08, having a ring I I8 for pressing it outwardly, also outwardly directed circular flanges |I9 and |20 against which there are located spring-retaining rings I 2| and |22 for supporting between them a helical spring |23. The grommet air valve |I1 is located within a chamber |24 formed in the valve casing 95. The valve casing has a venting port 95a for the grommet air valve I|1 leading to the space between the movable wall 86 and the end plate 85. There is also a similar port 95h for venting the grommet vacuum valve |08.

It will be apparent from the foregoing description that when the pedal is in fully released position and the power unit is inoperative the valve rod 43 is normally urged to the right by the reaction of the spring |00 at one end against the bushing 98, fastened to the valve casing shell 85 secured to the wall 86, and at the other end against the valve element IOI to thereby urge the valve element |0I, secured to the rod 43, to the right to unseat the flange |01 of the valve element IGI from the flange IIO of the grommet vacuum Valve |03 and to seat the flange |I6 of the valve element IGI on the flange I I9 of the air valve I I1 to thereby permit a vacuum connection from the left side of the wall 86 to port 99, chamber |05 and passageway |06 to the right side of the wall 8S. Upon initial slight movement of the rod 43 to the left by the plunger 21, as hereinafter described against the action of the spring |00, the valve element |0I will also be moved in the same direction to close the valve |01, IIO to interrupt the Vacuum connection, the slight movement of the rod 43 and valve element IUI being ineffective to open valve II6, II9, this stage of operation being shown in Fig. 2 wherein the valves |01, |I0 and II6, II9 are illustrated in their lapped positions. Upon further movement of the rod 43 to the left by the plunger 21, as hereinafter described, and thereby the valve element IUI the flange IIS of the valve element IOI will be unseated from the flange II9 of the grommet air Valve I I1 to permit the flow of air from the chamber 54 of the plunger 48 through the chamber |05 and passageway |06 to the right side of the wall 86 to effect movement of the wall 86 and rod 43 to the left as well as the piston 41 which places the liquid under pressure in the cylinder 5 I.

In the operation of my invention, it being assumed that there isa Vacuum received by the power unit from the manifold 1I by means of the pipe 10 into the interiorof the cylinder 68, when it is desired to apply the brakes, manual pressure is applied to the pedal'l which, accordingly, moves the master cylinder piston 6 to close the liquid compensation port 8 and thereby convey the hydraulic liquid under manual pressure tothe opening II in the powerunit. The valve I8 being initially'unseated from the valve seat 20 by the square stem I1 located against the stop I6 so as to press the tapered valve to the left against the force of the valve spring 23, the hydraulic :duid from the manual pressure pipe le will be conveyed initially past the valve I8, 20, through the ports 28, annular chamber 29, inclined passageway 30 and longitudinal passageway BI through the delivery port 32 and thence by the pipes 56, 51 and 58 to the front and rear wheelbrake cylinders 59 and 65, thus seating the brakes and alsopijoviding means whereby, at any time, the

manual hydraulic pressure can be applied to the, said brakes even when Athe power from thetpower unit is notr eifective for any reason. Thesaid manual hydraulic pressure, however, substantially immediately thereafter, moves the manual plunger 2'Ito the left, thus moving the squared stem I'I away from the stop it and seating, the valve I8 011 its Seat iii, the vaive I8, 2o thus acting asta cut-oir valve to disconnect the manual pressure liquid from being supplied thereafter from the pipe I8 to the brake lcylinders 59 and G. Continued manual pressure of the hydraulic fluid will thereafter move the manual plunger 21 to ther left so that` the valve rodJiB isA actuated thereby to seat the vacuum valve flange I? against the flange I i@ of the grommet vacuumvalve ISB. It will be understood that previous to this time the iiange Iii will have been normally maintained spaced away from the flange lie by the spring H19 so that, normally, before the actuation of the plunger 2 the vacuum received in the vacuum port iis will pass from the left face of the movable wall 85 to the right face thereof by means of the annular chamber 55 and the port H16. As stated above, however, when the iiange I 01 becomes seated on the flange I Iii of the grommet vacuum valve |88 the vacuum connection leading to the right face of the movable wall Se will thus become interrupted. This stage of the operation of the valve mechanism is shown in Fig. 2 wherein it may be seen that an initial manual hydraulic pressure exerted on the plunger 2 will eect a small movement of the rod d3 and valve element IBI to the left which will in turn cause the flange I! of the valve element IGI and iiange I IQ of the valve HI8 to assume a lapped position to interrupt the vacuum connection between the chambers on opposite sides of the walls 85- while failing to disrupt the lapped position of the fiange I I of thevalve element IGI and flange IIS of the valve Iii. After-this, upon further manual pressure beingexerted by means of the valve rod d3, the nange iI 6 onthe valve element I ilI will then become unseated from the flange IIS of the grommet air valve I Il', whereas before this time, and even when the power unit is not under manual actuation from thepedal I, the air valve HS, las will have been y.in closed position. The unseating of the air valve l it, I le will admit atmospheric air from the inlet port d to the annular chamber 45, thence through the holes 53 to the longitudinal passageway 54 in the power plunger 48, and thence through the valve I I, I I9 to the right face of the movable wall 8, thus moving the wall 86 to the left and carrying with it the power piston 41' which thereafter places the liquid under pressure, which is increased according tothe relative diameters ofthe wall 85 and the piston e?, so as to deliver the liquid under pressure by the delivery port 32 and the pipes 56, 5l` and 58 to the wheel brake cylinders 59 and 60 of the frontV and rear wheels of the automobile, respectively. i

Upon releasing the manual pressure, on the pedal I slightly and thereby the manual4 hydraulic pressure acting on the plunger 2T, the plunger 21 will be slightly moved to the right by the spring d which allows rod 43 in engagement withtlfll plunger Hand valve element Il to be movediin the same direction by the action of the spring. [0B so that the valvel I I6, H9 will become seated to close oif the admission of air from the chamber 54 of the plunger i3 to the chamber IE5 Vand passageway I and to the `right side of the piston 86 while thevacuum valve flanges Il and AIIi will remain seated preventing the admission ofA vacuum to the 4chamber H35 and to the right side of the piston 86, so as to maintain the particular desired pressure as applied to the wheel brake cylinders 53 and di). Upon further release of the manual pressure from the pedal I, however, the manual hydraulic pressure is released .on the plunger 21 and the latter will thereupon be moved to the Alimit of its travel to the right by itsspring 4D allowing the rod 43 and valve element .IGI to move to the right due to the action of the spring ld so that the vacuum valve IG'I, III) will b e opened, and, as the valve I It, I Iaremains closed, the movable wall 8S will again be submerged in the vacuum which isnow present on both sides thereof. In thisway by always maintaining the vacuumv on the left face of the movablewall 8,6 and applying more or less, as desired, of the atmpspheric pressure tothe right face of the movable wall 8e, the desired amount ofthe braking eiort is applied to the wheel cylinders` 59. and 6e.

While I have described my invention above in detail, I wish it to be understood that many changes may be made therein without departing from the spirit of the same.'

1- A power unit comprising a casing, a movable. wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side Vof the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power piunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall.

2. A power unit comprising a casing, a movable wall therein, a connectionv on the power unit adapted to be connected to a source of pressure differing from the atmospheric-pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to ther movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between theairvent and the movable wall and having a cylinder, and a hydraulic means for controlling said valvemechanism comprising a valveoperating rod passing through and beyond the power plunger for controlling the access of said pressure and air to move said movable wail.

3.l A power unit comprising a casing, a movable wall therein, a connection on the power` unit adapted to be connectedto a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an

air v entlocated on the other side of said wall, a

valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valve-operating rod coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall, provided with a valve element, and said valve mechanism having a vacuum valve and an air valve cooperating with said element.

4. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure diiering from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod passing through and beyond the power plunger for controlling the access of said pressure and air to move said movable wall, provided with a valve element, and said valve mechanism having a vacuum valve and an air valve cooperating with said element.

5. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected t the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall, provided with a valve element, and said valve mechanism having a rubber grommet vacuum valve and a rubber grommet air valve cooperating with said element.

6. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanismvfor controlling the application of said pressure to the movable walla power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod passing through yand. beyond the power plunger for controlling the access of said pressure and air to move said movable wall, provided with a valve element, and said valve mechanism having a rubber grommet vacuum valve and a rubber grommet air valve cooperating with said element.

7. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall, provided with a valve element, and said valve mechanism having a rubber grommet vacuum valve and a rubber grommet air valve cooperating with said element, each of said grommets having spring-separated anges.

8. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall. an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod passing through and beyond the power plunger for controlling the access of said pressure and air to move said movable wall, provided with a valve element, and said valve mechanism having a rubber grommet vacuum valve and a rubber grommet air valve cooperating with said element, each of said grommets having spring-separated flanges.

9. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a plunger and cylinder, a manual plunger, and a valve-operating rod, operated by the manual plunger, coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall.

10. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an Vair vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a plunger and cylinder, a manual plunger, and a valve-operating rod, operated by the manual plunger, passing through and beyond the power plunger for controlling the access of said pressure and air to move said movable wall.

11. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a plunger and cylinder, a hydraulic cut-ofi valve moved by the hydraulic means, a manual plunger, and a valveoperating rod, operated by the manual plunger, coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall.

12. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to `be connected to a source of pressure differing from the atmospheric pressure located at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a plunger and cylinder, a hydraulic cut-off valve moved by the hydraulic means, a manual plunger, and a valveoperating rod, operated by the manual plunger, passing through and beyond the power plunger for controlling the access of said pressure and air to move said movable wall.

13. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a Valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall on said other side between the air vent and the movable wall andhaving a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod coaxial with the power plunger for controlling the access of said pressure and air to move said movable wall, having a valve element mounted on said rod, said valve mechanism having a vacuum valve and an air Valve cooperating with said element.

14. A power unit comprising a casing, a movable Wall therein, a connection on the power unit adapted to be connected to a source of pressure diiering from the atmospheric pressure located on said casing at one side of the movable Wall, an air vent located on the other side of said wall,

a valve mechanism for controlling the application of said pressure to the movable wall, a power plunger for delivering hydraulicv pressure connected to the movable wall on said other side between the air vent and the movable wall and having a cylinder, and a hydraulic means for controlling said valve mechanism comprising a valveoperating rod passing through and beyond thc power plunger for controlling the access of said pressure and air to move said movable wall, having a valve element mounted on said rod, said valve mechanism having a vacuum valve and an air valve cooperating with said element.

l5. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source or pressure differing from the atmospheric pressure located on said casing at one side of the movable wall, an air vent located on the other side of said wall, a valve mechanism for controlling the application of said pressure and air to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall and having acylinder, and a hydraulically controlled plunger having therein and within the power plunger a valve rod to operate the valve and located coaxially with regard to said valve.

16. A power unit comprising a casing, a movable wall therein, a connection on the power unit adapted to be connected to a source of pressure differing from the atmospheric pressure located at one side of the movable wall, an air vent 1ocated on the other side of said wall, a valve mechanism for controlling the application of said pressure and air to the movable wall, a power plunger for delivering hydraulic pressure connected to the movable wall and having a cylinder, and a hydraulically controlled plunger having therein and within the power plunger a valve rod to operate the valve and located coaxially with regard to said valve, said power plunger having an air passageway leading to and coaxial with said valve.

EDWARD A. ROCKWELL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,604,545 Bragg Oct. 26, 1926 1,623,557 Rybeck Apr. 5, 1927 1,679,762 Bragg Aug. 7, 1928 2,260,491 Stelzer Oct. 28, 1941 2,322,063 Schnell June 15, 1943 2,340,817 Hurst Feb. 1, 1944 2,365,471 Ingres Dec. 19, 1944 2,366,520 Griffith Jan. 2, 1945 2,374,545 Ingres Apr. 24, 1945 2,401,892 Stelzer June 11, 1946 2,406,328 Gunderson Aug. 27, 1946 

